Monumnets of history are not so important in this topic. I can recommend something interesting, which is Hel Peninsula in northern Poland. Interesting for its natural enviroment, fantastic beach, dunes, location (big cities after a bay), lots of bars, "Fokarium" (seals'' pools) and a lot of other attractions.
travel to Poland I visited Poland last year with my uncle and brother who was born and grew up in Warsaw. We absolutely loved it in Warsaw and Krakow, especially seeing the salt mines and concentration camps. Poland is also great if you're a war buff since there are lots of WW2 and nazi history to be learned. For that, it's best you go to the Warsaw Uprising museum.
what to see in Poland I recommend visiting the Białowieza Forest. It's an ancient forest located north of Poland (near the border of Belarus) like no other forest you will see anywhere in Europe as it's the last remaining primeval forest left in Europe. Also, dont miss paying a visit to Gory Stołowe (The Stołowe Mountains) Mountains, Marienburg Castle in Malbork, Auschwitz-Birkenau death camps and, of course, Warsaw Old Town.
WWII history in Poland if you're WWII history buff, you will find that there is more sites to see in Poland than Auschwitz. For instance, in Warsaw you have the Warsaw Uprising museum and the Katyń Massacre Museum. Along Gdańsk you will find many WWII battlefield sites; while in Wolfsschanze, you can see Hitler's old nazi headquarters. There are also remains of the nazi concentration camps in places like Stutthof, Treblinka, Lublin, Bełzec, and Rogoznica.